It is well-known in the art to install fluid-flow conduits consisting of either porous ropes or blind holes, each by themselves, in the filter layers of a slip-casting mold. Even with these conduits, such filter layers have exhibited problems including non-uniform fluid-flow properties and poor mold strength. Heretofore, such problems have been considered unavoidable in the art. These problems and the improvements in casting molds in accordance with the present invention are explained in detail in the comparative example and working examples set forth in the present specification.